Let’s just pause, just for a minute and think through the implications of our actions today, so that this does not spiral out of control - US Representative Barbara Lee, 14 September 2001 The use of force is prohibited in international law. This simple but fundamental legal principle can be obscured in a geo-political context littered with conflict and threatened conflict where the exceptions are more often seen as the rule. Relatedly, there is a tendency to dismiss international law as a ‘marginal enterprise’ at moments of political crisis [1, p26]. This is why, in the immediate wake of the September 11 attacks, legalistic objections to the United States’ use of force against the perpetrators (and enablers) of these attacks could not help but sound reedy and off-key. However, twenty years later, the world is confronted by images of Afghanistan tumbling back under Taliban control, this time against the tragic backdrop of a military operation that cost 175,000 military and civilian lives and more than 3.2 trillion US dollars. It may be thought at this point that international legal arguments come too late. Yet, for international law, ‘hindsight is a necessary vice’.1 The practice of states, even that forged in heated times of war and crisis, can harden into enduring legal principles unless objected to or criticized in its aftermath. In this short essay, we examine the legal justifications for the military intervention in Afghanistan and consider the potential dangers in allowing these justifications to endure as part of the legal framework governing the use of force in international relations. Article 2(4) of the UN Charter, often described as the Charter’s cornerstone, provides that ‘All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations’ [2, p.xii–xiii]. In the ordinary course of things, the use of force against a state to achieve regime change, such as seen in Afghanistan in 2001, would be a manifest violation of the Charter. It may even amount to an unlawful use of force warranting higher censure as an act of aggression.2 Yet there are exceptions. First, the prohibition does not cover the situation where the government of a state consents to the use of force by another state within its territory [3]. Second, the Charter establishes a collective security framework, vesting ‘primary responsibility’ in the UN Security Council for the maintenance of international peace and security, and allowing the Council to authorize measures including the use of force where ‘necessary to maintain or restore international peace and security’. Third, Article 51 of the Charter notes that nothing in the Charter impairs the right of a state to use force in individual or collective self-defence in the event of an armed attack until the Security Council is able to take necessary measures. These three circumstances—consent, Security Council authorisation, or self-defence—are the only circumstances in which the use of force is not prohibited in international relations. Each of these justifications has its own elements and limitations. The US intervention in Afghanistan was justified on the basis of the doctrine of self-defence and, at least initially, faced few objections.3 Yet despite (or perhaps because of) the initial wide support, US action in Afghanistan has indelibly affected contemporary understandings of the doctrine of self-defence, and generated a number of variants of the traditional doctrine. This has happened to the extent that it has become common to divide analysis of self-defence (and indeed jus ad bellum more broadly) into pre- and post-9/11.4 Christine Gray’s seminal volume on International Law and the Use of Force notes that that ‘the US invasion of Afghanistan…led to a fundamental reappraisal of the law on self-defence’ [4, p200]. Below, we analyse these variants and assess the extent to which they impacted the authority, purpose, expectations, cooperation with and acceptable collateral damage in the context of the Afghanistan intervention. 1 Borrowing from Hilary Mantel’s description of the historian’s situation. 2 See definition in Rome Statute, Art 8 bis. 3 See reference to objections (on the basis of a preference for UN approval) by Cuba, Belarus and the Organization of the Islamic Conference of Foreign Ministers [3, p630–631]. 4 See, for example, the three parts of Use of Force in International Law [4] divided between (I) The Cold War Era; (II) the Post-Cold War Era; and (III) the Post 9/11-Era. Electronic copy available at: https://ssrn.com/abstract=4189376 Hovell and Hughes 3 LSE Public Policy Review DOI: 10.31389/lseppr.53 I. RUSH TO UNILATERAL ACTION: THE ‘FIRST OPTION’ VARIANT ‘Two opportunities stand above all others. First was the chance to convince the Taliban to hand over Osama bin Laden before the outbreak of war. Second was the opportunity to include the Taliban in the new political settlement. In both cases, the urgency of the moment overcame diplomacy’. - Carter Malkasian, 2021 Prior to 9/11, it was ‘self-evident and generally recognized’ that self-defence was only available as an action of last resort [5]. This ‘last resort’ requirement is a component of the principle of necessity. The most famous articulation of this doctrine derives from the Caroline Affair in 1837. Following this incident on the Niagara River, which involved the United States, Great Britain, and the Canadian independence movement, correspondence between US Secretary of State Daniel Webster and UK Foreign Secretary Lord Ashburton recorded that a state must show ‘a necessity of self-defence, instant, overwhelming, leaving no choice of means and no moment for deliberation’. The ‘last resort’ criteria, or the requirement to show ‘no choice of means’, is usually described in terms of an obligation to establish the non-availability of measures other than the use of force. However, the broader interpretation is that a state can only resort to self-defence when there are no other ‘realistic’ alternatives, including the non-availability of the other justifications for force, such as host state consent or Security Council authorisation. This interpretation suggests a hierarchy between the three available justifications for the use of force: first, state consent; second, Security Council authorisation; and third, self-defence.5 This positioning of self-defence as an option of last resort is seemingly justified by Article 51’s qualification that nothing shall impair the inherent right of self-defence ‘until the Security Council has taken measures necessary to maintain international peace and security’. A little-discussed aspect of the US response to 9/11 is that it seemingly upended this hierarchy. On 12 September 2001, the UN Security Council passed Resolution 1368, which seemed to immediately cede the ground to the United States, recognizing ‘the inherent right of individual or collective self-defence in accordance with the Charter’. It has been suggested that this reflected a deliberate and strategic preference on the part of the US, which elected for unilateral over multilateral action despite clear Security Council ‘readiness to take all necessary steps’ in Security Council resolution 13686 [6, p.635–636, 7]. This suggestion does not rest upon a sufficiently nuanced assessment of the Council’s reasoning. It is important to recall that in the moment, it was not only the Americans who were deeply shaken, but the international community as well. There had never been a terrorist attack of the magnitude, complexity and scope of 9/11, and even though the US and its allies had been closely tracking al Qaeda since the late 1980’s, their militaries, intelligence services and law enforcement had all missed critical indicators and warnings [8]. Furthermore, the relationship between the Taliban and al Qaeda had been matters of Security Council concern since 1996 [9]. Following the 1998 embassy bombings in Nairobi and Dar es Salaam, the effort assumed global importance, and the Clinton administration worked aggressively through diplomatic, intelligence and law enforcement channels to find a way to bring Osama bin Laden to justice [9 p121–126,205–207]. Subsequently, the Security Council passed four resolutions between 1998 and 2001 that specifically cited the threat from al Qaeda and declared the supporting actions of the Taliban government in Afghanistan to be a threat to international peace and security [10–13]. These resolutions were the foundation for the diplomatic activity that immediately followed the 9/11 attacks, including Resolution 1368. They indicate that while willing to act unilaterally, the US was aware that the transnational nature of al Qaeda’s networks and operations still demanded a multilateral approach. 5 According to Bruno Simma’s edited Commentary on the UN Charter, ‘the right of self-defence embodied in Art. 51 is only meant to be of a subsidiary nature’: 804. Adil Haque has gone so far as to describe self-defence as an ‘exception’ to Security Council authorisation: https://www.justsecurity.org/70987/the-united-nations-charterat-75-between-force-and-self-defense-part-two/. 6 Criticism of the US decision not to follow a multilateral approach were made by Cuba, Belarus and the Organization of the Islamic Conference of Foreign Ministers: [6 p630–631]. See related criticism in Delbrück, ‘The Fight Against Global Terrorism: Self-Defence or Collective Security as International Police Action’ (2001) 44 German Yearbook of International Law 9; Fassbender, ‘The UN Security Council and International Terrorism’ in Bianchi, Enforcing International Law Against Terrorists (2004), at 83, 88–89. Electronic copy available at: https://ssrn.com/abstract=4189376 Hovell and Hughes 4 LSE Public Policy Review DOI: 10.31389/lseppr.53 The question remains as to whether the ‘last resort’ threshold had been reached. It is clear that the law enforcement measures authorized in Resolutions 1267 [11] and 1333 [12] had not yet fully been exhausted. Both resolutions authorized the use of measures to halt the funding of Bin Laden’s and al Qaeda’s operations, but ‘there was as yet no coordinated U.S. Governmentwide strategy to track terrorist funding and close down their financial support networks’ [8 p119]. More problematically, there is also a strong counterfactual if we consider the availability of diplomatic options. Although such alternatives appeared to have been exhausted, the urgency of the moment and unprecedented international unity following the 9/11 attacks may have created a new opening for negotiations with the Taliban. According to former Bush administration officials, even though his national security council had concluded that any attack on al Qaeda would have to take out the Taliban as well, President Bush was not initially ready to commit to a course of action that would lead to regime change [8 p315, 14]. Instead, Bush at first maintained his position that if the Taliban would agree to turn al Qaeda leaders over to the US, close all terrorist camps, free foreign prisoners, and comply with UN Security Council resolutions, the US would leave the regime in place [9 p332–333, 14]. By September 18, as Secretary of State Powell lined up support for an eventual invasion of Afghanistan, Pakistani interlocutors reported that Taliban leader Mullah Omar had considered the US proposal, and ‘was not negative on all these points’ [9 p333]. Bush did not expect the Taliban to acquiesce, but in that moment, it was not yet an unrealistic option. With patience and sustained strategic pressure, diplomacy may have worked. Historian Carter Malkasian, a US State Department official in Afghanistan who later served as political advisor to the commander of the NATO forces, exhaustively researched the Taliban’s decisionmaking process in the early days following September 11. Malkasian concludes that while there may never be a definitive answer on whether a diplomatic solution could have been reached, there is strong evidence that–but for a combination of miscommunication, US political imperatives and the Bush administration’s fear of further attacks—a negotiated solution would have been possible [15]. Events overtook such an opportunity. On the evening of September 11, Bush had privately declared that the US would punish not just the perpetrators of the attacks, but those who harboured them as well [9 p330]. Over the days and weeks that followed, his resolve hardened and expanded to encompass the broader aim of ‘the elimination of terrorism as a threat to our way of life’ [9 p331]. Meanwhile, communicating through the Pakistanis, Mullah Omar agreed